In burst demodulators for radio signals, the pulling speed of PLL (phase locked loop) should be increased to accurately demodulate burst signals. For this reason, in a conventional method for estimating a phase in a burst demodulator, the phase of a burst signal is estimated, and the phase is used as an initial value of VCO (voltage controlled oscillator) in PLL. In this case, the phase of the burst signal is determined based on correlation of received burst signals determined using a parallel correlator.
Thus, according to the conventional method for estimating a phase in a burst demodulator, in demodulation of a burst signal, the phase of a burst signal is estimated based on correlation of received burst signals determined using a parallel correlator, the estimated phase is utilized as the initial value of VCO in PLL to increase the pulling speed in PLL.
According to the conventional method for estimating a phase in a burst demodulator, however, since the phase is estimated by determining correlation of burst signals in a parallel correlator, a memory capacity corresponding to a value obtained by multiplying the number of preambles by the number of samples is necessary. This poses a problem of an increased size of the circuit. SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a method for estimating a phase in a demodulator which can accurately demodulate a received signal without the necessity of increasing the size of the circuit and the memory capacity.
According to the first feature of the invention a method for estimating a phase in a demodulator, comprises the steps of: estimating a phase of a demodulated signal, obtained by demodulating a received signal, based on integrated values of the predetermined number of samples of a plurality of symbols constituting a preamble of the received signal; and
feeding the phase of the demodulated signal as an initial phase into a voltage controlled oscillator (VCO) in a phase locked loop contained in a demodulator for outputting the demodulated signal. PA1 converting the pseudo-synchronously detected signals to digital signals; PA1 integrating the digital signals with respect to the predetermined number of samples; PA1 latching the signals integrated with respect to the predetermined number of samples at predetermined timing; PA1 detecting the maximum value of the in-phase component and the orthogonal component in the latched signals; and PA1 estimating, from the maximum value, a phase to be used as an initial phase value of a phase locked loop (PLL) in a demodulator for the burst signal.
According to the second feature of the invention, a method for estimating a phase in a demodulator comprises the steps of: pseudo-synchronously detecting a received burst signal by an in-phase component and an orthogonal component of a local oscillation signal;